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Old 8th March 2009
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Default Jumbo Frames

Hi all,

I have a firewall with a vge0 interface doing firewalling/routing between Gigabit VLANs. I am trying to configure the mtu of the interface to support larger frames.

The NIC is a VIA VT6122

According to the vge man page:

Quote:
The MAC supports IPv4 transmit/receive IP/TCP/UDP hardware
checksum offload, VLAN tag insertion and stripping, a 64-entry CAM filter
and a 64-entry VLAN filter, 64-bit multicast hash filter, 4 separate
transmit DMA queues, flow control and Jumbo frames up to 16K in size.
The VT6122 has a 16K receive FIFO and 48K transmit FIFO.
No matter what I try though I can't seem to change the MTU. I always get

"ifconfig: SIOCSIFMTU: Invalid argument"

What are the valid sizes for the MTU value? I want to set it to a max of 9K as that is the largest frame size my switch will support.

Also does one change the MTU on the real interface or the VLAN interface?
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Old 8th March 2009
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Jumbo frame support for vge(4) was disabled in the 4.0 release, I don't think it was ever enabled again.

See revision 1.25 of src/sys/dev/pci/if_vge.c.

You may want to send a message to one of the mailing lists, perhaps one of the developers would be willing to fix it.
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Old 8th March 2009
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Cheers BSDfan666, if I get any handy feedback from the developers I'll report back.

I have three other RealteK RTL8110SC NICs on the same box so I might swap things around to one of those.
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Old 13th March 2009
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Even when you do find a card that will work with jumbo frames, I would recommend you only stick to regular jumbo frames (9000 or less) rather than super jumbo frames (9000 to 64K). It's not that they aren't ever used, but here's a good summary of "what's out there" that supports a particular frame size-

http://darkwing.uoregon.edu/~joe/jumbo-clean-gear.html

Basically most gear you are going to run into uses 9000 MTU or less, so you should likely configure your card to the same. Apparently at that MTU, NFS should perform nicely (it uses 8k packets.)

http://osdir.com/ml/os.openbsd.tech/.../msg00249.html

Happy reading.
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Old 15th March 2009
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Cheers ai-danno. I'll be sticking with 9K frames because that's all the switch will support however I might have to go lower as I think one of my machines will only do 7K. But having a rethink about everything.

Happy St. Patricks Day (well weekend )
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Old 15th March 2009
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First off, when an Irishman wishes you Happy St. Patrick's Day, that's just really really cool (to an Irish-American such as myself, anyway.) So Happy St. Patrick's Day to you, as well!

On your jumbo frame issue, it seems as though you understand a salient point that bears mentioning for anyone else referencing this thread- all devices in your network that intend on taking advantage of jumbo frames of any size will need to all match the same size together. So in this example, if one device supports 7K sized frames, all devices in the network should appropriately be set to 7K as well, or frames they transmit to that particular host will eventually will become fragmented, hurting performance.

The only way around this 'lowest-common denominator' approach for flexible MTU based on host is through the use of VLAN's. Each VLAN can have it's own configured MTU, instead of relying on a single MTU used by all in the network. This extends the complexity of your underlying network setup, though, and necessitates a connecting switch capable of VLAN Trunks (not the ether-channel-style trunking (aka, bonding)) so that each switch port can transmit on multiple VLANs simultaneously.
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Old 15th March 2009
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OT: My great grandmother was from Ireland, she immigrated to Canada.. St. Patrick's day is celebrated on the 17th March here though.
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Old 16th March 2009
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Quote:
Originally Posted by ai-danno View Post
First off, when an Irishman wishes you Happy St. Patrick's Day, that's just really really cool (to an Irish-American such as myself, anyway.) So Happy St. Patrick's Day to you, as well!

[...]
My pleasure, I hope you are enjoying the weekend. I know I am, although going to bed last night at 4am to get up for work this morning at 7 didn't help me start the week but two days off from the end of today will help a ton!

Quote:
Originally Posted by ai-danno View Post
[...]

On your jumbo frame issue, it seems as though you understand a salient point that bears mentioning for anyone else referencing this thread- all devices in your network that intend on taking advantage of jumbo frames of any size will need to all match the same size together. So in this example, if one device supports 7K sized frames, all devices in the network should appropriately be set to 7K as well, or frames they transmit to that particular host will eventually will become fragmented, hurting performance.
This is something that everyone is going to find out the hard way - or through a ton of reading! But definitely something that is a vital consideration when implementing the use of jumbo frames. I find the best thing to do is to start off at the manufacturers website for both your switch and network interfaces and get the data sheets for each. Find out the max jumbo frame size supported, if supported, and plan around the smallest-largest size that one device supports and try to match the rest everywhere else on the LAN.

Quote:
Originally Posted by ai-danno View Post
[...]
The only way around this 'lowest-common denominator' approach for flexible MTU based on host is through the use of VLAN's. Each VLAN can have it's own configured MTU, instead of relying on a single MTU used by all in the network. This extends the complexity of your underlying network setup, though, and necessitates a connecting switch capable of VLAN Trunks (not the ether-channel-style trunking (aka, bonding)) so that each switch port can transmit on multiple VLANs simultaneously.
I am actually using VLANs in my setup, here -> http://www.konundrum.org/lanbuild.pdf (Yes, it is a bit complicated for a home LAN :P ) The problem is I will be using jumbo frames across VLANs.

Quote:
Originally Posted by BSDfan666 View Post
OT: My great grandmother was from Ireland, she immigrated to Canada.. St. Patrick's day is celebrated on the 17th March here though.
That's because St. Patrick's day is the 17th of March :P That's funny, my grandfather was Canadian and moved to Ireland! He and his sister were separated very early in their lives. He lived most his life in Ireland and she in Canada.
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